Safety device for electric incandescent lamps



March 29, 1932. F ECKHARDT ET AL 1 9 SAFETY DEVICE FOR ELECTRICINCANDESCENT LAMPS Filed Jail; 23, 1929 0 ed across the incandescentfilament.

Patented Mar. 29, 1932 FRITZ EGKHARiDT AND MAX HOHNEKAMP, OF EISENACH,GERMANY SAFETY DEVICE FOR ELECTRIC INCANDESCENT LAMPS Application filedJanuary 23, 1929, Serial No. 834,572, and in Germany September 17, 1928.

This invention relates to the so-called safety devices for electricincandescent lamps connected in series to the supply. circuit. Suchsafety devices are provided with .5: resistances which are shuntedacross theincandescentfilament of each lamp and which, as long as thelamp is still good, that is to say as long as the voltage required forits operation is applied across its terminals, do not allow practicallyany current to pass through them, but which, when the filament of thelamp is destroyed and consequently a voltage substantially higher thanthat required for its operation is applied, become conductive and thusbridge over the destroyed filaments. p

More particularly the invention relates to safety devices in which theresistance consists of a large number of small particles of 2 metal,natural ores, metal sulphides, or metal oxides, which lie loosely nextto one another or are united together into a solid body.

Such safety devices have previously been manufactured, by disposing thevoltage sensitive resistance, more particularly the small particles orthe conglomerated solid body, in a hollow space of the base cap or inthe socket of the lamp. The accommodation in a hollow space of the lamp,however. causes great 80 difliculties in the new lamp sealing methods,

since in most cases a suitable space in the glass bulb itself is notavailable.

The mounting within the socket of the lamp had the disadvantage thatafter the safety device had comeinto operation at least once, the wholeof the socket could no longer be used.

The object of the present invention is to avoid these disadvantages. Theinvention consists in this that the voltage responsive resistance, whichpreferably consists of a large number of small particles is enclosed inan insulating casing which is provided with two contacts and togetherwith the said casing is accommodated as a whole in one of the fittingsleading the current to'the lamp, more particularly in the base cap or inthesocket .of the lamp and is connected in such a man,- ner with theleads that the resistance is shunt- The particles constituting theresistance may consist of metal, natural ore, which can be roasted, of ametal oxide, or a metal sulphide, of

a synthetic chemical compound which is the equivalent of a naturalroasted or non-roasted ore, for instance of roasted galena, or of ironhammer-scale (Fe O In the preferred form of construction, the safetydevice is mounted in the socket of the incandescent lamp and it isremovably secured therein, the electrical connection being also easilydetachable, for instance by means of springs, so that the safety device,that is to say the casing containing the resistance, can be easilyexchanged. I

Other essential features of the. invention will hereinafter be describedwith reference to the accompanying drawings, in which Fig. 1 illustratesin a section along the axis and on an enlarged scale, one form ofconstruction of the safety device which is especially suitable foraccommodationin the base cap.

Fig. 2 shows a section along the axis of an incandescent lamp in which asafety device as shown in Fig. 1 is mounted in the base cap.

Fig. 3 is a section along the axis and on an enlarged scale of a form ofconstruction of the safety device which is especially suitable foraccommodation in descent lamps.

Fi 4; illustrates a section along the axis of a soc et adapted to beequipped with a safety device according to Fig. 2.

Fig. 5 is an elevation of the socket according to Fig. 4 seen'from theside where the safety device is provided.

Fi 6 is a cross section along the line VI%7I of Fig. 4, seen from below,with a safety device according to Figure 3 inserted therein. 4

Referring to Fig. 1, 1 is a metal casing having the shape of a flatcylinder, the bottom '2 of which is provided with a large opening 3 inthe centre. An insulating disc 4 is'mounted on the bottom of the casing.The latter is filled with the material 5 constituting the resistance andwhich may consist of powdered roasted galena. An insulating disc 6 isplaced on the resistance filling, whichdisc is held the sockets ofincanso in position by the inner flange 7 provided on the casing 1. Aconducting wire 8 passes through the centre of the casing, theinsulating disc 4, the resistance filling and the insulating disc 6 andis connected to a small metal plate 9, which rests on the insulatingdisc 6. The resistance 5 is thus conductively connected with the casing1 as well as with the wire 8.

Referring to Fig. 2, 10 is the bulb of an incandescent lamp and 11 isthe metal'base cap thereof. 12 and 13 are the leads to the incandescentfilament 12 of the lamp, the lead 12 being conductively connected in theusual manner to the base cap 11. A safety device as illustrated in Fig.1 is mounted within the hollow space of the base cap, being for instancecement'ed therein. The lead 13 of the lamp is conductively connected tothe small plate 9 of the said safety'device, being for instance solderedthereto and the wire 8 of the safety device is conductively connected,for

instance by soldering, to the usual foot contact 14 of the base cap. Thewall of the casing 1 is conductively connected by means of a separatewire 15 to the lead 12.

When a plurality of such lamps are connected in series with one anotheracross the supply circuit, for instance eight lamps, across a supplycircuit of 110 v., then as long as the filaments of the lamps are stillgood, the current will flow through each lamp along the following path:14891312'-12 11. Between the wall 1 of the casing and the central wire8, there is a voltage of 110+8=14 v. and this voltage is not suffi--cient to render the resistance 5 conductive. However, when theincandescent filament is destroyed, the whole of the voltage of thesupply circuit, viz. 110 v. is applied between the wall 1 and the wire 8and this voltage is suflicient to render the resistance conductive andthus bridge over the gap which has been produced by the breakage of thefilament.

Referring to 'Fig. 3, 16 is a small tube of insulating material, 17 ametal cap for clos ing up the said tube, whilst 18 is a second closingcap'of metal for the said tube. The end of the tube lying next to thecap 11 is filled up -by a metal bolt 19 which passes through the cap 18and is screw-threaded, as shown at 20, beyond that cap. A knob or handle21 of insulating material is screwed on to the screw-threaded part 20 ofthe bolt. The space between the top end of the bolt 19 and the cap 17 isfilled with a powder 5', for instance powdered iron hammer-scale,

which does not allow the current to pass through as long as a smallvoltage is applied between the caps 17 and 18, for instance 10- 30 v.but which becomes conductive when a higher voltage, for instance morethan v. is applied between the caps 17 and 18.

' Referring to Figs 4-6, 22 is a cylindrical sleeve of insulatingmaterial forming the socket of an incandescent lamp. 23 is a partitionwall of insulating material provided in the lower end of the saidcylindrical sleeve. 24 is the screw-threaded part of the socket for theneck and 25 is a foot contact.

At approximately the height of the partition wall 23 the cylindricalsleeve 22 is provided with a hole 26, which lies transversely to theaxis and which is closed on the one side by a wall 27 and at the back bya bottom part 28, whilst it is open towards the front. The hole is sowide that a safety device according to Fig. 3 can be accommodatedtherein. In the proximity of the bottom 28, the hole 26 communicateswith an opening 29, which leads to the space below the partition wall 23whilst at about its centre the hole 26 communicates with an opening 30leading to the space above the partition wall 23.

A resilient metal strip 31, which is conductively connected with thescrew-threaded portion 24 of the neck passes through the opening 30 intothe hole 26, whilst a resilient metal strip 32, which is conductivelyconnected with the foot contact 25 by means of a bolt 33 passes throughthe opening 29 into the hole 26. The distance between the openings 29and 30 is such that when a safety device according to Fig. 3 is insertedinto the hole 26, the resilient member 32 comes in contact with the cap17 and the resilient member 31 in contact with thecap 18.

The operation of the device is as follows When such a socket isconnected in series with a plurality of other similar sockets and anordinary lamp is inserted in each socket and a current is passed throughthe lamps, the said current will flow from the neck contact of thesocket through the incandescent filament of the lamp to the foot contactof the socket. Between the neck contact and the foot contact andconsequently between the resilient members 31 and 32, as well as betweenthe caps 17 and 18, there is applied only the operative voltage of thelamp, for instance 14 v. and since for this voltage the resistanceconsisting of the powder 5' is not conductive, no current will flowthrough the safety device. However, when the filament of the lamp isdestroyed, the whole of the supply circuit voltage, for instance 110 v.is applied between the caps 17 and'18 and the powder 5 becomesconductive, with the result that the safety device bridges the gapproduced by the disconnection of the lamp and the other lamps continueto glow.

- The invention is not limited to the forms of construction hereinbeforedescribed. The

vided with two contact members which casing is of such a size that itcan be mounted in the base cap or socket of an incandescent lamp, sothat the safety device constitutes a self-contained unit which can beseparately manufactured and; be readily inserted into the position ofuse and be easily replaced.

'VVhat we claim is 1. As an independent article of manufacture, anelectric safety device comprising a fiat cylinder with conducting sidewall and insulating cover and bottom, a conducting wire passing throughthe said cover and bottom and projecting beyond the bottom, apulverize'd mass filling the hollow space of the said cylinder, whichmass is in conductive contact with the said conducting wall and wire,the said mass being such that it conducts the current only when thepotential difference between the said conducting wall and wire exceeds apredetermined value, said safety device being insertable in the fittingof an electric incandescent lamp, as and for the purposes set forth.

2. As an independent article of manufacture, an electric safety devicecomprising an insulating tube, a conducting cover and bottom therefor, amass filling up the space of the said tube and being in conductivecontact with the said cover and bottom, the said mass being such that itconducts the current only when there is a potential difference betweenthe cover and bottom which exceeds a predetermined value, said safetydevice being insertable in the fitting of an electric incandescent lampand said conducting cover and bottom being adapted to engageconductively contacts in said fitting, as and for the purposes setforth.

3. A socket for electric incandescent lamps comprising an insulatingsocket body having a neck contact and a foot contact, an insulatingcasing with two contact pieces mounted in the said socket body andcapable of being exchanged, a resistance in the said casing inconductive contact with the said two contact pieces, a removableconductive connection from the one contact member to the neck contactand a removable conductive connection from the other contact member tothe foot contact, the said resistance being such that the currentisconducted onl when a voltage is applied between the said contactmembers which is greater than the operative voltage of the incandescentlamp.

4. A socket for electric incandescent lamps comprising an insulating,substantially cylindrical hollow body, an insulatingpartition wall whichdivides the said hollow body into an upper and a lower space, a neckcontact on the inner wall of the upper space, a foot contact on the sideof the partition wall facing the upper hollow space, an outer wall whichis transverse to the axis of the cylindrical insulating body and whichforms with the wall of the insulating body a pas sage open at one end,the said passage having an opening whlch communlcates wlth the lowerhollow space of the insulating body and an opening which is incommunication with the upper hollow space of the said insulating body, abottom at the other end of the passage, an insulating sleeve in the saidpassage, the said insulating sleeve having contact members at its twoends, a resilient member fixed to the neck contact which passes throughthe opening which is in communication with the upper space, the saidresilient member being resiliently connected to the one contact memberof the sleeve, a conducting member which is secured to the foot contactand passes through the opening which is incommunication with the lowerspace into the said passage and is resiliently connected with the othercontact member of the sleeve, a resistance in the insulating sleeve inconductive contact with the two contact members, which resistance issuch that it conducts the current only when a voltage is applied to thecontact members which is higher than the operative voltage of theincandescent lamp. 7

5. A safety device for electric incandescent lamps comprising aninsulating container independent from the base cap and the socket of thelamps and adapted to be loosely inserted into the fitting of the lamp,at least one conducting part on the outside of said container, twocontact members in the said container and a resistance filling up theinterior of the container and consisting of a large number of smallparticles, the said resistance being in conductive contact with the saidcontact members and being such that it conducts the current only whenthe potential difference between the said contact members exceeds apredetermined value.

In testimony whereof we have signed our names to this specification.

FRITZ ECKHARDT. MAX HOHNEKAMP.

